Hydroxybenzoic acid as pH buffer and corrosion inhibitor for alkali metal silicate-containing antifreeze compositions

ABSTRACT

This invention relates to single-phase antifreeze or coolant concentrates comprising a major proportion of at least one alcohol, at least one water-soluble silicate, and an organic basic pH buffer and corrosion inhibitor comprising at least one hydroxybenzoic acid. The concentrates can be used without dilution but are preferably used, upon dilution with water. The concentrates are generally diluted for use in with about 25 to about 90 percent by weight of water based upon the total weight of the concentrate. The alcohol is preferably ethylene glycol. The alcohol-based antifreeze and coolant compositions of the invention are effective in the protection against corrosion of all metals and alloys used in industrial processes and are especially effective when used to inhibit the corrosion of aluminum internal combustion engine and radiator components.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to alcohol based antifreeze and coolantcompositions containing corrosion inhibitors for use primarily inwater-circulating systems such as internal combustion engines, heatexchangers, cooling towers, and the like.

2. Description of the Prior Art

Antifreeze concentrates containing alcohols such as ethylene glycol arecommonly diluted with water to prepare cooling system compositions forinternal combustion engines in order to depress the freezing point ofwater. It is known that the alcohols utilized gradually decompose in thecooling system to produce acidic products which lower the pH of thecoolant. It is also known that metallic surfaces in internal combustionengines which are in contact with such coolants become seriouslycorroded and that the corrosion effects generally become progressivelyworse as the pH of the coolant decreases. The recent tendency toward theuse of aluminum in internal combustion engines, for instance, aluminumcylinder heads, aluminum water pumps and aluminum radiator cores, makesdesirable improved, less corrosive antifreeze compositions. It has alsobeen recognized in the art that antifreeze compositions are mostdesirably single-phase systems which have good shelf stability such thatwhen such concentrates reach the consumer prior to dilution with waterto form the coolant composition, such compositions contain the properproportion of each phase and exhibit no gelation.

Numerous antifreeze compositions are known in the art which containcorrosion inhibitors and inhibitors for preventing decomposition of thealcohol utilized, for instance, ethylene glycol. These corrosioninhibitors and stabilizers for alcohol decomposition include bothorganic materials and inorganic materials. Illustrative of the organicmaterials that have been used in antifreeze compositions are guanadine,citrates, coal tar derivatives, petroleum bases, thiocyanate, peptones,phenols, thioureas, tannin, quinoline, morpholine, triethanolaminetartrates, glycol mono-ricinoleate, organic nitrites, mercaptans,sulfonated hydrocarbons, fatty oils, triazoles, mercaptobenzothiazoles,phenothiazine, and piperazine. Illustrative of the inorganic materialsthat have been used as corrosion inhibitors are sulfates, sulfides,fluorides, hydrogen peroxide, alkali metal chromates, nitrites,phosphates, borates, tungstates, molybdates, carbonates, and silicates.

Silicates, particularly alkali metal silicates and certain silicones andsilicate-silicone copolymers, have been suggested for use in antifreezecompositions to retard the corrosion of metal surfaces of internalcombustion engines as disclosed in U.S. Pat. Nos. 3,341,469; 3,337,496;3,312,622; 3,198,820; 3,203,969; 3,248,329; 3,265,623; 3,121,692; andothers. While it has been found that compositions containing alkalimetal silicates are effective corrosion inhibitors for metals ininternal combustion engines, especially aluminum, the use of suchmetallic silicates in antifreeze compositions is disadvantageous sincethese antifreeze compositions have poor shelf life and/or use life, thatis, a tendency to gel and form precipitates on standing prior todilution of antifreeze concentrates by the consumer or during use as acoolant. With respect to the water-soluble organo-silicones andwater-soluble silicate-silicone copolymers which have been suggested foruse in antifreeze compositions, it has been found that it would bedesirable in such systems if greater reserve alkalinity could beincorporated into the system thereby reducing the corrosion tendency onlong term use as a coolant.

In U.S. Pat. No. 2,832,742, there is disclosed an ethylene glycol basecoolant for use in automobile radiators containing a corrosioninhibiting composition composed of equal parts of para tertiary butylbenzoic acid and a high molecular weight aliphatic carboxylic acidderived from a petroleum fraction. In U.S. Pat. No. 2,197,774 there isdisclosed the use of aromatic nitro-hydroxy compounds wherein the nitroand hydroxy groups are directly attached to the aromatic nucleus orpositioned only on a side chain. In Canadian Pat. No. 990,060 there isdisclosed ethylene glycol based antifreeze compositions containingalkali metal silicates and alkali metal nitrites as corrosion inhibitorswhich are buffered at a pH of about 9 to about 10.5. There is noindication in any of these references that hydroxybenzoic acids such asparahydroxy benzoic acid are effective pH buffers and corrosioninhibitors in such systems.

SUMMARY OF THE INVENTION

There are disclosed single-phase antifreeze and coolant concentratescomprising at least one alcohol selected from the group consisting ofmethanol, ethanol, propanol, ethylene glycol, diethylene glycol,triethylene glycol, propylene glycol and glycerol; a corrosioninhibiting amount of at least one water-soluble metal silicate; and, asan organic basic pH buffer and corrosion inhibitor, a hydroxybenzoicacid or mixtures thereof.

Preferably said alcohol is ethylene glycol and preferably the antifreezeconcentrates of the invention are utilized as coolants upon dilutionwith water in internal combustion engines including those enginescontaining aluminum parts, for instance, aluminum cylinder heads. By theincorporation of at least one hydroxybenzoic acid into antifreezecompositions containing metal silicates, the pronounced tendency of themetal silicates to gel can be overcome. The organic pH buffers andcorrosion inhibitors of the invention are especially advantageous ascompared to the alkali metal borate buffers.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The compositions of this invention contain a novel corrosion inhibitingorganic basic buffer which is a hydroxybenzoic acid or mixture thereof,preferably para hydroxybenzoic acid. The meta and ortho forms of (mono)hydroxybenzoic acid as well as the dihydroxybenzoic acids are alsouseful, i.e., 2,6- and 2,4-dihydroxybenzoic acids. The use of suchbuffers serves to maintain the pH of the antifreeze or coolantcomposition above a pH of about 9 to about 11, preferably a pH aboveabout 9.5 to 10.5 in order to minimize corrosion which increases withthe decreasing pH of the antifreeze system. Additionally, where awater-soluble metal silicate is utilized as a component of theantifreeze composition, the buffering of the pH by the hydroxybenzoicacid compounds of the invention serves to maintain the metal silicate insolution by preventing gel formation which increases with decreasing pHbelow a pH of about 9. While many basic pH buffers have been used in thepast in antifreeze compositions to maintain the pH above 7, the alkalimetal borate salt buffers preferred for use therein as taught by theprior art such as sodium tetraborate, sodium orthoborate, and sodiummetaborate are ineffective in preventing gel formation during use of theantifreeze where the antifreeze composition contains water-soluble metalsilicates.

The amount of the hydroxybenzoic acid basic pH buffer utilized in thecompositions of the invention depends to some extent upon the desiredshelf life of the antifreeze concentrate containing the buffer, theeffectiveness of the particular hydroxybenzoic acid selected and theproportions of the other components of the antifreeze concentratecomposition. Generally, amounts of the hydroxybenzoic acid buffercompositions of the invention range from about 0.1 percent to about 1.5percent by weight, preferably about 0.5 percent to about 1.2 percent byweight based upon the weight of the alcohol used in the antifreezeconcentrates of the invention. The use of lesser amounts of the buffersof the invention can result in a significant decrease in the pH of thecoolant in a relatively short use time whereas the use of greateramounts of the buffer can involve the expenditure of needless amounts ofmoney and possibly lead to insolubility problems. No advantage isgenerally gained by departing from the indicated proportions or from theuse of additional basic pH buffer materials known in the prior art.

The alcohols that are suitable for use in preparing the antifreeze andcooling compositions of the invention include both monohydric alcoholsand polyhydric alcohols. Thus, methanol, ethanol, and propanol as wellas ethylene glycol, diethylene glycol, triethylene glycol, propyleneglycol and glycerol are useful. Mixtures of these alcohols are alsouseful in the compositions of this invention. Ethylene glycol is anespecially useful alcohol. The alcohol and coolant concentrates of theinvention are useful as a heat transfer medium in the cooling systems ofinternal combustion engines both undiluted or upon dilution withrelatively large amounts of water. The antifreeze concentrates of theinvention are adapted to economical shipment and storage; theconcentrate being shipped to the point where it is to be used in dilutedform as a coolant. Water imparts desirable properties to both theconcentrate and coolant compositions of the invention since smallamounts of water tend to lower the freezing point of the concentratecomposition and large amounts of water improve the heat transferproperties of the coolant compositions. The antifreeze concentratecompositions of the invention can contain about 0.1 percent by weight toabout 10 percent by weight of water based upon the weight of theconcentrate. The concentrates preferably contain about 1 to about 5percent by weight of water, and most preferably about 2 to about 3percent by weight of water, based upon the weight of the concentrate.Generally the coolant compositions contain about 25 percent to about 90percent by weight of water based upon the total weight of the dilutedconcentrate. The pH of both the antifreeze concentrate compositions ofthe invention and the coolants diluted with the above larger amounts ofwater generally should be maintained at greater than about 9 to about 11in order that corrosion of metals with which the compositions come incontact will be minimized. Any alkali such as one or a mixture of thealkali metal hydroxides can be used to adjust pH.

Various additives known in the prior art can be added to the antifreezeconcentrate compositions of the invention or to the coolant compositionsin order to impart special properties thereto. For instance, antifoamagents, identifying dyes, pH indicators, conventional metal corrosioninhibitors, alcohol oxidation inhibitors, sealants which prevent leakageof the coolant from the coolant system, anticreep agents which preventseepage of the coolant into the crankcase of the internal combustionengine, and the like can be added to either or both the antifreezeconcentrates of the inventions or the diluted coolant compositions ofthe invention. It should be noted that, while the antifreeze and coolantcompositions of this invention are single-phase compositions, theaddition of various additives insoluble in the alcohol or in water canrender these compositions two-phase (for instance, the addition of aninsoluble defoamer or sealant additive which prevents leakage of thecoolant from the cooling system). While the antifreeze concentrates andcoolant compositions of this invention are particularly suitable for useeither alone or upon dilution with water as coolants suitable for use inthe cooling system of an internal combustion engine, the compositionscan be advantageously employed in other applications such as heattransfer fluids or hydraulic fluids.

The corrosion inhibiting, water-soluble metal silicates are well knownin the art. The silicates are used in the coolant concentratecompositions of the invention generally in a corrosion inhibitingamount, preferably about 0.05 to about 0.5 percent by weight based uponthe weight of the concentrate. The preferred water-soluble metalsilicates can be represented by the average formula

    M.sub.2 O(SiO.sub.2).sub.n

wherein M is an alkali metal and n has a value of about 0.5 to about 4inclusive. Illustrative of these silicates are the alkali metalorthosilicates, the alkali metal metasilicates, and the alkali metaldi-, tri-, and tetrasilicates. Specific examples of these silicates arepotassium metasilicate, sodium orthosilicate, potassium disilicate,lithium orthosilicate, lithium metasilicate, lithium disilicate,rubidium disilicate, rubidium tetrasilicate, mixed silicates such assodium and potassium metasilicates. The preferred silicates are sodiumand potassium silicates and the sodium and potassium metasilicates.These silicates are known in the art and are further described in U.S.Pat. No. 3,337,496, incorporated herein by reference.

The improvements in stability and corrosion inhibition resulting fromthe use of the hydroxy benzoic acid buffer compositions in combinationwith the alcohol and silicate components of the antifreeze concentratecompositions of the invention were discovered through evaluationutilizing laboratory tests. Certain of these tests are designed tosimulate field conditions.

The following test methods were used in evaluating corrosion resistanceof the antifreeze coolant compositions of the invention.

MODIFIED GLASSWARE TEST

This is a laboratory test for determining pitting corrosion of aluminumin aqueous alcohol antifreeze solutions such as are used in the coolingsystems of internal combustion engines. Coupons of 3003 aluminum alloyand 3003 aluminum alloy clad with 7072 aluminum alloy were stackedseparated by plastic insulators. In order to determine the tendencytoward crevice corrosion, a rubber hose useful in automotiveapplications was cut into sections similar in size to the aluminum alloycoupons and placed between the last two coupons on either end of a stackof coupons being evaluated for corrosion. The stack of coupons wasimmersed in an antifreeze solution containing 25 percent by weight of anantifreeze concentrate. Dilution with water was made, said watercontaining 300, 500, and 1000 parts per million chloride ionrespectively. The solutions were heated for a period of four hours at atemperature of 200° F., cooled for two hours and left at ambienttemperature conditions for six hours to constitute a single cycle. Thistwelve hour cycle was repeated for about two weeks. At the end of thetest period, the coupons were disassembled and rinsed with water andacetone and subsequently examined under the microscope. The antifreezeformulation under evaluation was given a rating depending upon theseverity of the pitting and crevice corrosion found.

THE ULTRASONIC CAVITATION ERROSION TEST

This is a laboratory test procedure for the evaluation of internalcombustion engine coolants to determine their capability to preventcavitation-erosion of aluminum test specimens using ultrasonic energy toproduce the cavitation effect. The test involves subjecting aluminumspecimens to the test conditions while totally immersed in a 15 percentcoolant solution during a period of 20 hours at a temperature of 82°±2°C. in an ultrasonic tank. Comparison is made of the average weight lossincurred by the specimens under test against the weight loss ofspecimens in a reference coolant solution. The average weight loss isdetermined to calculate the aluminum cavitation-erosion rating ofbetween 1 and 10, with a rating of 10 showing no corrosion. This testmethod corresponds with ASTM D-2966, incorporated herein by reference.

The following examples illustrate the various aspects of the invention.When not otherwise specified throughout this specification and claims,temperatures are given in degrees centigrade and parts, percentages andproportions are by weight.

EXAMPLE 1 (Comparative Example Forming No Part of This Invention)

Utilizing a modified glassware test, as is more fully described above,25 parts by weight of a reference antifreeze concentrate composition wasdiluted with 75 parts by weight of water containing respectively 300,500 and 1000 parts per million of chloride as sodium chloride.Thereafter, three aluminum alloy No. 3003 coupons measuring 2 inches by4 inches by 1/16 inch were placed in each of the above dilutedantifreeze concentrate compositions. The alloy coupons were insulatedfrom each other and placed 3/4 of an inch above the bottom of the beakerutilizing brass supporting structures. The solutions were heated fourhours at a temperature of 190° F. and then cooled to ambient temperatureover a period of two hours and allowed to remain at ambient temperaturefor six hours to make a 12 hour cycle which was repeated for theduration of the test which lasted a period of two weeks.

The reference antifreeze concentrate used in this example had thefollowing composition:

    ______________________________________                                        Ingredient              Parts by Weight                                       ______________________________________                                        ethylene glycol (antifreeze grade)                                                                    95.8                                                  borax, pentahydrate     1.10                                                  trisodium phosphate     0.42                                                  sodium metasilicate     0.16                                                  sodium nitrate          0.21                                                  sodium mercaptobenzothiazole (50% active)                                                             0.50                                                  sodium hydroxide (50% active)                                                                         0.44                                                  defoamer (PLURONIC® L-61 Polyol)                                                                  0.03                                                  water (deionized or soft water)                                                                       1.33                                                  ______________________________________                                    

After a two week period, the appearance of the alloy coupons indicatedthe presence of a few pits and a moderate extent of crevice corrosion.PLURONIC L-61 Polyol is an ethylene oxide, propylene oxide blockcopolymer having a molecular weight of about 1750 and 10 percent byweight ethylene oxide residue content, sold by BASF Wyandotte Corp.

EXAMPLE 2 (Comparative Example Forming No Part of This Invention)

Example 1 was repeated utilizing the same reference antifreezecomposition as used in Example 1 but omitting the borax, pentahydrate inthe amount of 1.10 parts by weight.

The results after two weeks indicate that the corrosion tendency asindicated by pitting was about the same as with Example 1. However,crevice corrosion was slightly worse. Streaks of white corrosionproducts formed above all freshly exposed aluminum.

EXAMPLE 3

Example 1 was repeated except that the borax, pentahydrate in the amountof 1.10 parts by weight was eliminated and para hydroxybenzoic acid inthe amount of 0.5 parts by weight was substituted therefor.

After the two week period of test, the results as indicated byappearance show that the presence of para hydroxybenzoic acid completelyeliminated the white streaks above freshly exposed aluminum surfaces aswell as the pitting corrosion shown in Examples 1 and 2. In addition,the crevice corrosion was significantly improved over that shown inExamples 1 and 2.

EXAMPLE 4 (Comparative example forming no part of this invention)

Utilizing the cavitation erosion-corrosion test of ASTM D-2966, acontrol antifreeze composition was evaluated having the followingcomposition:

    ______________________________________                                        Ingredient            Parts by Weight                                         ______________________________________                                        Ethylene Glycol (antifreeze grade)                                                                  95.0                                                    Borax, Pentahydrate   1.0                                                     Sodium Nitrate        0.2                                                     Tolyl Triazole        0.2                                                     Water                 3.6                                                     ______________________________________                                    

This control antifreeze had a pH of 8.4 and upon evaluation in thecavitation erosion-corrosion test was given a rating of 3.3.

EXAMPLE 5

The procedure of Example 4 was repeated utilizing an antifreezecomposition similar to that utilized in Example 4 except that the waterwas not utilized and 1 part by weight ortho hydroxybenzoic acid wasadded. The composition had a pH of 4 and was rated -4.6.

EXAMPLE 6

The procedure of Example 4 was repeated utilizing an antifreezeconcentrate similar to that used in Example 5 except that thecomposition contained 1 part by weight of para hydroxybenzoic acid wassubstituted for otho hydroxybenzoic acid. The composition had a pH of8.4 and was rated 8.1 when tested in the cavitation erosion-corrosiontest.

EXAMPLE 7

The procedure of Example 4 was repeated using an antifreeze concentratesimilar in composition to that utilized in Example 5 with the exceptionthat the borax component was eliminated entirely and the compositioncontained 1 part by weight of ortho hydroxybenzoic acid. The compositionhad a pH of 8.4 and upon testing for cavitation erosion-corrosion wasgiven a rating of 8.1.

EXAMPLE 8

Utilizing the cavitation erosion-corrosion test of ASTM D-2966, anantifreeze concentrate was evaluated for resistance to cavitationcorrosion. The antifreeze concentrate had the following composition:

    ______________________________________                                        Ingredient            Parts by Weight                                         ______________________________________                                        Ethylene glycol (antifreeze grade)                                                                  95.0                                                    Sodium metasilicate (Na.sub.2 SiO.sub.3 5H.sub.2 O)                                                 0.4                                                     Tolyl Triazole        0.2                                                     Ortho hydroxybenzoic acid                                                                           1.0                                                     ______________________________________                                    

The composition had a pH of 10.5 and upon evaluation utilizing thistest, was given a rating of 4.0.

EXAMPLE 9

The procedure of Example 8 was repeated utilizing an antifreezecomposition similar to that utilized in Example 8 except that instead ofortho hydroxybenzoic acid, the composition contained 1 part by weight ofpara hydroxybenzoic acid. The antifreeze composition had a pH of 10.5and upon evaluation for cavitation corrosion, was given a rating of10.0.

EXAMPLE 10

The procedure of Example 8 was repeated utilizing an antifreezecomposition similar to that disclosed in Example 8 with the exceptionthat the composition additionally contained 0.5 part by weight of orthohydroxybenzoic acid and 0.5 part by weight of para hydroxybenzoic acid.The composition had a pH of 10.5 and was given a rating of 9.9 uponevaluation for cavitation corrosion.

While this invention has been described with reference to certainembodiments, it will be recognized by those skilled in the art that manyvariations are possible without departing from the scope and spirit ofthe invention and it will be understood that it is intended to cover allchanges and modifications of the invention disclosed herein for thepurposes of illustration which do not constitute departures from thespirit and scope of the invention.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A single-phaseantifreeze or coolant concentrate consisting essentially of a majorproportion of at least one alcohol selected from the group consisting ofmethanol, ethanol, propanol, ethylene glycol, diethylene glycol,triethylene glycol, propylene glycol and glycerol, an amount of about0.05 to about 0.5 percent by weight of at least one water-solublesilicate and, as a pH buffer and corrosion inhibitor, about 0.1 to about1.5 percent by weight of at least one hydroxybenzoic acid selected fromthe group consisting of ortho and para hydroxybenzoic acid, wherein saidwater-soluble silicate has the formula:

    M.sub.2 O(SiO.sub.2).sub.n

wherein M is an alkali metal and n has a value of about 0.5 to about 4,and wherein said buffer serves to maintain the pH of said antifreezeabove about 9 to about
 11. 2. The composition of claim 1 wherein saidwater-soluble alkali metal silicate is selected from the groupconsisting of alkali metal orthosilicates, alkali metal metasilicates,alkali metal tetrasilicates, alkali metal trisilicates and alkali metaldisilicates.
 3. The composition of claim 2 wherein said concentrateadditionally contains about 0.1 percent to about 10 percent by weight ofwater based upon the weight of said concentrate.
 4. The composition ofclaim 3 wherein said alcohol is ethylene glycol, and said hydroxybenzoicacid is para hydroxybenzoic acid.
 5. A coolant composition consistingessentially of the coolant concentrate of claim 1 and about 25 percentto about 90 percent by weight of water based upon the total weight ofthe diluted concentrate.
 6. The composition of claim 5 wherein saidwater-soluble alkali metal silicate is selected from the groupconsisting of alkali metal orthosilicates, alkali metal metasilicates,alkali metal tetrasilicates, alkali metal trisilicates and alkali metaldisilicates.
 7. The composition of claim 6 wherein alcohol is ethyleneglycol, and said hydroxybenzoic acid is para hydroxybenzoic acid.